2ktx
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(New page: 200px<br /><applet load="2ktx" size="450" color="white" frame="true" align="right" spinBox="true" caption="2ktx" /> '''COMPLETE KALIOTOXIN FROM ANDROCTONUS MAURETA...)
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Revision as of 10:33, 21 November 2007
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COMPLETE KALIOTOXIN FROM ANDROCTONUS MAURETANICUS MAURETANICUS, NMR, 18 STRUCTURES
Overview
Kaliotoxin (KTX) is a natural peptide blocker of voltage-dependent K+, channels. The 3D structure of a truncated analogue of KTX (Fernandez et, al. (1994) Biochemistry 33, 14256-14263) was determined by NMR, spectroscopy and showed significant differences from structures, established for other related scorpion toxins. A recent publication with, the structure of the complete toxin (Aiyar et al. (1995) Neuron 15, 1169-1181) did not confirm these differences. In this communication we, report NMR data for KTX at pH 3.0, 5.5 and 7.2 and the 3D structure, obtained from data at pH = 5.5. Complete KTX displays a folding similar to, that of other toxins with an alpha-helix and a beta-sheet linked by two, disulphide bonds. The pKa of His 34 is anomalously low (4.7-5.2 depending, on the buffer) owing to its interaction with two Lys residues (including, the essential Lys 27), the charged N-terminus and the side chain of Met, 29. Charged residues are placed symmetrically with respect to an axis that, approximately coincides with one of the principal components of the moment, of inertia of the toxin. His 34, which occupies a well-defined position, between two conserved Cys, is located on the centre of a layer of charged, groups. Positively and negatively charged residues are found at the same, position in related toxins. It is suggested that electrostatic effects, modulate the distances between positive charges in flexible side chains, contributing to the fine tuning of the selectivity toward different, channel subclasses and that the approximate coincidence between the moment, of inertia and the charge axis facilitate the approach of the toxin to the, channel. The very low pKa of His 34 implies that it will be completely, unprotonated at physiological pH.
About this Structure
2KTX is a Single protein structure of sequence from Androctonus mauretanicus mauretanicus. Full crystallographic information is available from OCA.
Reference
3D structure of kaliotoxin: is residue 34 a key for channel selectivity?, Gairi M, Romi R, Fernandez I, Rochat H, Martin-Eauclaire MF, Van Rietschoten J, Pons M, Giralt E, J Pept Sci. 1997 Jul-Aug;3(4):314-9. PMID:9262650
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